Hello everybody,
Since two weeks now, we have massive sensitivity problems with our QTRAP5500 (AB Sciex). We are running an established sMRM method for the detection of eicosanoids on the machine (in negative mode), which worked very well for years now. So two weeks ago, we were preparing for another series of samples, having good looking quality controls (eicosanoid mixture) in terms of peak intensity. But measurement of the first sample, suddenly shows an intensity decrease by multiple orders of magnitude and testing the same quality control again, suddenly also shows an intensity decrease by factor 10.
We were then going for a complete front end cleaning procedure, cleaning the curtain plate, orifice plate and the QJet Ion giude. After this, tunning with PPGs as well as our eicosanoid quality control looked very good again.
But then the whole thing started over again: We measured two samples and observed this massive drop in intensity (before you may ask: we do an SPE extraction with all samples prior to measurement to remove possible contaminants). We performed cleaning again, using the Alconox solution this time, as recommended in the Instrument Frond End Cleaning manual. Further we also tested for contamination of the Q0, but the sensitivity after polarity switching remains constant, so we didn’t perform a Q0 clean so far.
However, advanced cleaning also didn’t solve the problem. This time we measured some older samples, of which we know, they didn’t cause any problems on the machine before, but again after 5 samples the intensity gradually decreases to over 70 % of the first measured standard mixture.
So we are running out of ideas, what we could do to solve the problem. The method ran stable the last years, without sensitivity loss over several 100 samples. Does anybody have a suggestion what could cause the problem or any suggestion what else we could try to solve it?
Hi Jacqueline,
did you test the ESI voltage at the tip of your probe? In many cases sudden problems indicate a hardware problem. Check the power supply of the ESI-source. You can easily measure the voltage with a multimeter and a high voltage tester (http://www.amprobe.com/Amprobe/usen/Electrical-Testers/High-Voltage-Test---TIC-Tracer/AMP-HV231-10A.htm?PID=73249). Voltage readbacks of the software are often misleading because they are not correct. Some years ago we had a similar problem with the ESI probe of a Waters TOF system. The cause was a hair crack in the probe. Via this hair crack we had loss of voltage and therefore a decreased signal intensity.
If the ESI source is not the problem, you have to measure the voltages of your ion guide/filters. This is maybe a little bit tricky but with a good technical service manual you can check it. But be careful: Inside a mass spectrometer is an area of high voltage!
Another two reasons for massive sensitivity loss: clogged sample cone or a clogged splitter capillary
Regards Markus
P.S.: Related to this topic I've found some links:
https://www.chromforum.org/viewtopic.php?t=11650
https://sciex.com/support/knowledge-base-articles/lost-sensitivity-on-your-triple-quad-or-qtrap-you-may-need-to-optimize-your-cem-detector-parameter-1481142998734
https://www.researchgate.net/post/There_is_a_4000_QTRAP_intensity_decrease_What_is_the_reason
Hi Jacqueline.
I agree with Markus, this is throuble could be clogged capillary. You could remove capillar for your probe and conect it in a hplc pump outside, aply 1,0 ml/min flow. If you don't see the spray, it´s this your problem.
I hope this help you.
Hello everybody,
first of all, thanks to all for your answers.
At least I can exclude a clogged ESI capillary, as we observe a continuous and stable spray.
Measuring the Voltage wouldn't be that easy at the moment, as we simply don't have a high voltage tester and need to organize this one first. However, if the voltage of the probe isn't correct, wouldn't I then expect a constantly decreased intensity (and not a gradual decrease with samples over time)?
Of course I also contacted the Sciex helpdesk, but they only recommend to perform a drift test so far to check for contamination of Q0. This is what we already did and - as expceted - testing again also didn't suspect for contamination in this region.
Markus, thank you also for the links. The last two I already knew and we also checked for sensitivity loss of the detector. But accoridng to the test results, increase in detector voltage isn't necessary.
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